Cleaning boiler tubes of digesting heat exchangers used in alum earth processing

Abstract

The invention relates to plant operations for increasing the cycle times of heat exchangers by the digestion of the aluminium oxide content of a slurry according to the Bayer technology, said slurry consisting of bauxite and sodium aluminate liquor, using an equipment in which the material is heated stepwise and in more parallel material streams, then the material streams are combined and further heated, or combined and kept at the same temperature, or after combination further heated and kept at the same temperature, characterized in that a part of the parallel material streams is slurry, another part of same is aqueous sodium hydroxide solution, preferably sodium aluminate liquor containing sodium hydroxide, or water, and the parallel material streams are exchanged in the heat exchangers in a cyclical manner.

What is claimed is: 
     
       1. A method of operating a plant for digesting aluminum oxide in a sodium aluminate liquor, said method comprising the steps of: (a) passing a slurry of aluminum oxide mineral in a sodium aluminate liquor through a plurality of tubes of at least one tube-type digester while heating said tubes of said digester and recovering digestion liquor downstream from said digester;   (b) passing a cleaning liquid selected from the group which consists of sodium aluminate liquor, sodium hydroxide solution and water through at least one other tube of said digester while the latter is heated concurrently with the other tubes thereof and other tubes of said digester conduct said slurry therethrough and recovering the heated cleaning liquid downstream of said digester, whereby deposits formed in the tube traversed by the cleaning liquid during previous passage of slurry therethrough, are dissolved in the cleaning liquid;   (c) cyclically applying step (b) to each of the tubes of the digester while conducting said slurry as in step (a) through each tube previously subjected to step (b); and   (d) combining the digestion liquid with the cleaning liquid recovered from step (b).   
     
     
       2. The method defined in claim 1 wherein, prior to combining in step (d), the cleaning liquid is partly in a vapor phase. 
     
     
       3. The method defined in claim 1 wherein said cleaning liquid is a sodium aluminate liquor containing sodium hydroxide. 
     
     
       4. The method defined in claim 1 wherein subsequent to step (d) the combined digestion liquor and cleaning liquid is heated.